Electric lamp base



May 5, 1964 G. J. EDWARDS ELECTRIC LAMP BASE Filed May 31, 1962 Inven h01- Geowe J. Edwavds b3 02% His Att vnes p j 3,131,986 v A v ELECTRICLAMP BASE George J. Edwards, l?ainesville, Ohio, assignor to General Electric Company, a corporation of NewYork Filed May 31, 1962, Ser. No. 198;957 i 2- Clainis. -(Cl. 339-146) l invention-relates generally' to electric lamps, and

more particularly to bases therefor. Still more particularly, the" invention relates to bases of the three-contact type generally employed withincandescent lamps of the three-way type having a major and a minor filament and adapted for use in sockets having a switching arrangement for energizing the filaments individually, or both in multiple,- so as to. obtain "three levels of illumination.

The conventional three-contact base comprises a threaded metal. shell having a web of insulating material closing one end. and projecting outwardly therefroni and carrying an intermediatevv flat ring vcontactjconcentric with the axis of the shell, and a centrally disposed endor center contact. n some instances, erratic operation of the lamp has 'beenexperie'nced in commercially availablej sockets their other ends-to respectivelead wires and 6. The

as, for example, operation at only one light level'br'flicker- I ingbetweenlevels r Accordingly, it is a principal objectof this invention to prov de an improved construction of the base which will minimize malfunctioning of the lamp in conventional sockets. 1

Briefly stated, it was found that some sockets departed radically from the average in critical. operating dimen sions, preventing reliable operation of the conventional base. A contributing factor is the fact that a contact post in many of the sockets is so constructed that the vertical pressure of the conventional intermediate flat ring contact on the base forces the said contact post inwardtoward the center contact of the socket. In some'sockets this causes the post and center contacts of the socket to come into engagement with each other, resulting in operation of the lamp at the same light level on three switch positions. This effect is overcome by employing a base intermediate ring contact of frusto conical shape to thereby force the con-.

tact post of the socket outwardly away from the socket center contact. However, inemploying a frusto conical ring having a slope sufficient to readily and effectively force the socket contact post outward, there are occasions when the socket post contact is too short' and is located too far outward toward the outer edge of the frusto coni ical'ring contact to be firmly engaged by the said outer lnaccordance with the invenedge of the ring contact. tion, reliability of operation'is materially increased by employing a base intermediate'ring contact of composite form including a frusto conical inner portion and a fiat planar outer portion whereby to eifect outward wedging vide firm engagement ofthe flat outer portion with socket contact .posts which are short and are located toward the outer edgeof the base ring contact.

A further, correlative, function of the flat planar portion 18 is to limit the depth of travel of the base into the socket before the ring contact meets the contact post socket-shell .14 passes beyond the thread available on the 1T his results in a need for more hand torque make the contact'less positive when it occurs. Thispossibilityjis increased by the existence of a large number of sockets in "which the threaded metal shell portion is distinctly longer than that in the average socket.

' action and firm engagement ofthe frusto conical portion with properly located socket contact posts, and also pro- 16, in the case just described. *If the depth of travel is not so limited, meeting of the ring 10 and the contact post i 16 may not occur before the outer edge of the threaded 3,131,986 Patented May 5, 1964 ICC ' FIG. 2 is an elevation, in section along theline 2-2 in FIG. 3, of the base on an enlarged scale;

FIG. 3 isa top end orplan view of the base; and

FIG-."4 is a fragmentary section of the base on a still further'enl'arged scale. i

, Referring to FIG.'1 of the drawing, the lamp illustrated therein comprises a glass bulb 1 containing major and minor filaments 2 and 3. Both filaments 2 and 3 are connected at one end to a common lead wire 4 and at bulb'l has'att'ached to its end a" base comprising a screw threaded metal shell 7 having one end closed by a web 8 of insulating material such as a thermosetting organic plastic. Thew'eb 8 carries an end contact or eyelet 9 and an intermediate ring contact 10 concentric with the axis of the shell- 7. lhe common lead wire 4 extends exteriorly of the bulb through a conventional stem tube 11 and is connected to the base shell 7. The'lead wires 5 and 6 are connected to respective end and intermediate contacts-9 and' 10 by quantities of solder Z1 and 12 (FIG. 4) filling the aperture in the eyelet contact 9 and a thread ing aperture 12' in ring contact '10.

The socket shown in FIG. 1 is of conventional construction and comprises a metal husk 13 containing a screw threaded shell contact 14, flexible center contact 15 and intermediate post contact 16 which are supported from an insulating block (not shown) which also contains theswitchmechanism (also not shown). The'shell contact 14 is connected to one terminal of a source of current supply, and the said switch mechanism may be arranged to successively connect the other terminal to,

firstly, both the end and intermediate contacts 15 and 16 for high level illumination, secondly, contact 15 alone for medium level illumination, and thirdly, intermediate contact 16 alone for low level illumination, followed by an off position.

In accordance with the invention, the base intermediate ring contact 10 comprises an inner frusto conical portion 17 which is enlarged in a 'direction'away from the end contact 9 and terminates in a flat or planar portion 18 in aplane transverse to the axis of the shell 7. As here illustrated the fiat portion 18 of the contact 10 is of square outline with its corners 19 bent under and embedded in the body of the insulating web 8.

Upon screwing the base 7 into the socket shell 14, the

socket post, contact 16 normally engages the sloping sides of the conical portion 17 of the base ring contact 10, thus forcing the said post 16 outwardly away from the socket centercontact 15. This is in contrast to the action of a plain flat base ring contact wherein the vertical pressure on the post contact l tends to force it inwardly toward the socket center contact 15,Wlth consequent likelihood even though thepost 16 also be of shorter than normal length whereas, even with the base screwed in tightly as far as possible, the said post may nevertheless'fail to en gage with a simple frusto conical ring contact evenif the conical surface 17 were extended downward to be below the post 16. In order to make sure of a positive wiping,

wedging action of the conical surface 17 against the socket contact post 16, it .isdesirable that the angle of the taper be, at least 20?, preferablyv about25. I

As indicated in FIG. 4, the solder globule 12 on the ring contact 10 is preferably finished off level with the contour of the sloping andflat surfaces of the contact, and the solder, globule 21 on the centertcontact is finished flat with its surface at a precise distance relative to the, sur- [face of the ring contact 10,- 1

This distance is an important factorin minimizing defec tive electrical contact at either .the ringcontact or the center contact when variations insocket dimensions are considered. v

As also shown in FIG. 4, that portion of the surface of the insulating plastic web 8 which is located between the inner edge of the ring contact loll and the center'contact 9, is preferably grooved as shown at 20 thereby increasing the length of any surface leakage pathbetween those contacts. In addition, this groove facilitates the 7 4 insulating material closing one end of said shell, a centrally arranged end contact and an intermediate annular ring contact carried by portions of said web projecting beyond said shell, said ring contact comprising an inner frusto conical portion concentric with the axis of said shell and enlarged in. direction away from said end contact toward said shell and terminating at its larger end in an outer fiat portion transverse. to said shell axis.

2. An electric lamp base comprising a shell, a web of insulating material closing one end of said shell, a centrally arranged end contact and an intermediate annular ring contact carriedi'by; portions of said :web projecting beyond said, shell, saidringcontact@comprising an inner frusto conical portion, concentric with the axis of said molding of the plastic when it .is undesirable to extend the I frusto conical surface to meet the end contact 9, Unless the frustov conical surface is interrupted before it would meet the end contact 9, it is not possible to simultaneously maintain the desired vertical distance between the end contact surface and the 'ringscontactsurface,-,the desired horizontal or annular width of the frustoaconical surface shell-and enlarged in adirection away from said end contact toward said she'll andterminating at its larger. end in-an;outer'zflat'rprortion transverse. to, said shell axis, the surface of that-portion of said web located between the proximate edges of said end contact and ring contact being formed with an, annular groove therein.

' References Cited the-file of this patent UNITED STATES PATENTS 55171989 j o r. 23, 1894 2,150,431. V M M y 30, 3 ,15 ,328' W i rnqr et 1 wte-l-v-A g- 9 FOREIGN PATENTSi 492,268

Ge lan r Feb. 20, 1930 

1. AN ELECTRIC LAMP BASE COMPRISING A SHELL, A WEB OF INSULATING MATERIAL CLOSING ONE END OF SAID SHELL, A CENTRALLY ARRANGED END CONTACT AND AN INTERMEDIATE ANNULAR RING CONTACT CARRIED BY PORTIONS OF SAID WEB PROJECTING BEYOND SAID SHELL, SAID RING CONTACT COMPRISING AN INNER FRUSTO CONICAL PORTION CONCENTRIC WITH THE AXIS OF SAID SHELL AND ENLARGED IN A DIRECTION AWAY FROM SAID END CONTACT TOWARD SAID SHELL AND TERMINATING AT ITS LARGER END IN AN OUTER FLAT PORTION TRANSVERSE TO SAID SHELL AXIS. 